Stedt



UNITED STATES MAXIMILIAN nnnnsrnur, or TZSGHEOHELN-NIEDERLANSITZ, PRUSSIA,

GERMANY.

MANUFACTURE AND PRESERVATION OF ARTICLES OF GYPSUM, STUCCO, OR THE LIKE.

SPECIFICATION forming part of Letters Patent No. 314:,114, dated March 17 1885.

Application filed January 10, 1885. (No specimens.) Patented in Belgium October 17, 1884. No. 66,629; in England October 17, E84 No. l3,76l, mid in Italy December 6, 1884, XXXIV, 455.

, To all whom it may concern.-

' STEDT, doctor of philosophy, a subject of the King of Prussia, residing at Tzscheoheln-Niederlansitz, Prussia, German Empire, have invented certain new and useful Improvements in and Relating to the Manufacture and Preservation of Articles of Gypsum, Stucco, or the like, (for which I have obtained Letters Patent in Belgium, No. 66,629, dated October 17, 1884; in Great Britain, No. 13,761, dated October 17, 1884., and in Italy, No. 455, dated December 6, 1884;) and I do hereby declare the following to be a full, clear, and exact description oftheinvention, such as will enable others skilled in the art to which itappertains to make and use the same.

This invention relates to a process of increasing the density of articles or objects made of gypsum, terra-cotta, stucco, soft stone, and other like substances, which articles are more i or less frangible, liable to injury, and cannot be cleansed without destroying the finer and sharper lines thereof.

The object of the invention is to increase the density or homogeneity of such articles, harden the same so as to render them less liable to injury, adapt them to be readily cleansed by washing with water, and,'if desired, to impart to such articles or objects an intensely black color.

Various attempts have been made to increase the homogeneity of objects of art and other articles or ornaments made of materials of the nature of those enumerated above,witha view to harden such articles or objects and render them less frangible and less liable to abrasion and injury. The methods heretofore resorted to .have, however, not only the great disadvantage of being very complicated and at the same time very costly, but the object aimed at is thereby only partially attained. These methods consist, essentially, in impregnating the objects with chemicals that form in part insoluble combinations which fill up the pores of the material. To this end it has been. proposed to impregnate the object alternately with lime 'or baryta water and silicate of pot-assa or solutions of sulphates in order to grad ually fill up the pores of the material with the resultant insoluble silicate or sulphate. Although this method is correct in principle, yet there are produced soluble by-products or combinations which greatly affect the result sought, and which could only be counteracted by special treatment or manipulation. This has been effected by lixiviation in water or by conversion of the alcoholic portion thereof by means of silicious hydrofluoric acid into the corresponding silicious fluor alkali, any remaining porti0n-principally carbonic acid and chlorine-being then removed by baking or calcining. Irrespective of the danger of an imperfect elimination of the soluble elements from the article or object treated the process itself is toocomplex for practical application and too costly. In all the processes proposed these difficulties and disadvantages have been encountered, and chiefly for the reason that cold solutions of lime or baryta were employed.

By my improved process all these disadvantages are overcome, and my invention consists, essentially and broadly, in the use of hot saturated solutions-thatis to say, highlyconoentrated solutions of barium or strontium hydrate alternately with such free acids or metal salts thereof as will prevent the formation of soluble by-products, and thereby avoid all further treatment. The free acids referred to are carbonic acid, sulphuric acid,'silicicacid anhydrite, chromic acid. or phosphoric acid, all of which I have found to produce the desired results.

In carrying out my invention I proceed as follows: The object is carefully dried and heat ed to about 80 or 100. "It is then washed or painted with a'hot saturated solution of bariuni hydrate until the material is saturated that is to say, until said material will absorb no more of the solution. In the process of washing or painting, an ordinary brush or a sponge can, of course,-not be employed, and I employ a glass brush that is to say, a brush made up of threads of glass.

Inasmuch as it is very difficult, if not impossible, to make a brush of the proper size that will be durable, I unite a number of small or thin glass brushes by placing them in a row or in concentric circles in a suitable glass holder, and cementing the same in position by means of a cement made of oystcrshells and soluble glass, (silicate of potash.) In this manner I can obtain either flat or round brushes of any desired thickness. During the partial coolingofthesolution,whileapplyingthesame, isolated crystals of caustic baryta are formed on the surface of the article or object treated, which may be readily removed with a soft brush. The object or article saturated with the hot solution of barium hydrate is then exposed to an atmosphere laden with carbonic acid and dried. To this end chambers may be used, into which carbonicacid gas is introduced, or which are provided with means for generating the gas.

Ifitis desired to obtain a particularly homogeneous or solid mass,the described operation may be repeated one or more times.

\Vhen any of the other acids above referred to are employed, the operation is reversed that is to say, the object is first washed or painted with the acid solution,then dried,and afterward saturated with the hot solution of barium or strontium hydrate. In this mode of procedure, the acid solution should be sufficiently attenuated to leave always a portion of the barium or strontium hydrate uncombined,which uncombined portion is afterward gradually neutralized by atmospheric carbonic acid.

The last above described mode of proceeding may be greatly simplified and at the same ti me better results obtained than by either one or the other of the processes set forth by treating the material from which the article is to be produced. This is effected by mixing or making up the material from which the article or object is to be made with the free-acid solution then making the article or object,and after drying the same treating it with the hot saturated solution of barium or strontium hydrate.

When a solution of'silicic-acid anhydrite is employed, it will be found best to add the baritum hydrate in a solid form to the mass, and instead of barium hydrate the cheaper calcium hydrate may be employed, this in view of the fact that the combination of the silicic acid with the baryta goes forward very slowly.

Instead of the solutions of the free acids above referred to, solutions of their metal salts may be employed; and in this respect it should be remarked that the reaction of the metal salts upon the barium hydroxide gives rise to the formation of insoluble metallic oxides or hydroxides besides the insoluble baryta salts. If the object so treated is, after drying, saturated with a hot solution of barium hydrate, a decomposition of the metal salts takes place and the metallic oxides or hydroxides separate from the insoluble baryta salt that fills the pores, and, as these oxides or hydroxides are also insoluble, they assist materially in the preservation of the article or object.

Articles or objects made from materials prepared with silicicacid anhydrite and barium 7c or calcium hydrate, as above set forth, may also be treated with the described metal-salt solutions.

It will be observed thatl have herein-above referred to the use of hot solutions of barium or strontium hydrate only for the reason that better results are obtained than by the pro posed method of treating objects of this class with cold baryta water. In the latter case but a comparatively small proportion of the barium hydrate enters into the reaction, be cause the calcium hydrate is much less soluble than the barium hydrate in the conversion of the barium-saturated gypsum into sulphate of baryt-a and calcium oxide, so that but a small proportion of sulphate of baryta and carbon ate of lime results from the chemical reaction, the hardening of the object being due almost exclusively tov the barium carbonate derived from the excess of barium hydrate. It is ob- 9o vious, therefore, that when cold baryta solutions are employed the more delicate and sharper lines of the object are liable to be ob literated or destroyed during the immersion of the object by reason of the partial solubility of the calcium hydrate formed during said in'r mersion, which is entirely obviated by the use of hot solutions, because the solubility of the calcium hydrate is at high temperatures greatly diminished. On the other hand, the de- I00 posit of the insoluble elements when cold solutions are employed is superficial only, the surface pores being completely closed when the operation is repeated several times, consequently absorption ceases, so that any at 05 tempt to further harden the surface by a repetition of the operation is fruitless. If, on the contrary, the object is heated to 80 or centigrade, and then treated with a hot solution, the latter will under atmospheric press- I 0 ure penetrate deeply into the material, and on cooling the barium hydrate crystallizes within the pores, and is there converted into barium carbonate, which conversion takes place very rapidly when the object is subjected to the ac- I15 tion of carbonic acid.

I have stated above that, if the material is made up with a solution of silieic-acid anhyvdrite, the barium hydrate may be added in a dry or solid form. I would state that this mode of proceeding may be reversedname-- ly, that the material maybe mixed up or prepared with a solution of barium hydrate and the silicic'acid auhydrite added in a dry or solid state, and preferably in the form offine- 5 ly divided orpulverized glassand this tends to even increase the density and resistance or strength of the object.

The strength or resistance as well as the density of the material may also be increased I 30 by mixing with gypsum or other like substances a substance which, either by chemical action upon the barium hydrate or by its inherent properties, will impartto the object formed of the compound the qualities sought. Thus, for example, glass, cement, kaoline, or other like substances, either separately or mixed or combined with marble-dust, witherite, heavy spar, or analogous substances, may be added to the gypsum and in proportion even as high as fifty per cent. without affecting the property of the gypsum to reproduce the finest or most delicate forms or designs.

It may be finally remarked that, when free sulphuric acid is employed, as above described a jet or intensely black color may be imparted to the object by the admixture of an organic substance-such as a saccharine substancewith the barium hydrate. This may be effected by adding from five to ten grams of sugar,for instance,to every one hundred cubic centimeters of water, and as much barium hydrate as the water will take up when slightly heated.

This solution is also applied ina hot state to the article or object, and when saturated the latter is slowly dried, so asto avoid as much as possible the formation of caustic baryta crystals. After drying the article or object is then washed with a solution of sulphuric acid, (about ten cubic centimeters of the acid to about one hundred cubiccentimeters of water,) and again dried in a temperature of 7 0 to 80 centigrade. The sulphuric acid gradually decomposes the sugar, and carbon is separated, which imparts to the object the black color. Instead of saccharine substances, other organic substances may be employed, which will be converted into carbon by the sulphuricacidas,forinstance,tartaric,acetic, and oxalic acid-in which case they may be used in the form of their respective barium salts.

Any article or object'made of gypsum, plaster otparis stucco, terra-cotta, or other analogous substance, when treated as described, may be washed with water without the least injury thereto, and may therefore be kept in a cleaner condition than has been possible heretofore.

Having now described my invention, what I claim is- 1. The process herein described of increasing the density of articles or objects made of gypsum, stucco, terracotta, and other analogous porous and frangible materials, and

adapting such articles or objects to be cleansed by washing with water, -by treatment with a hot saturated barium or strontium. solution,

and drying in presence of carbonic-acid gas.

2. The herein-described process of increasing the density of articles or objects made of gypsum, stucco, terra-cotta, and other analogous substances, and adapting such articles or objects to becleansed by washing with water, by mixing with the substance finely-pulverized glass, cement, kaolin, and other like substances, either separately or in gmbination,

or in combination with finely-pulverized marble, witherite, heavy spar, or other like substances,and treating'the obj ect made therefrom with a hot saturated solution ofa barium or strontium hydrate, and drying the same in presence of carbonic-acid gas.

3. The process herein described of increasing the density of articles or objects made of ing the density of articles or objects made of' gypsum, stucco, terracotta, and other analogous substances, and adapting such articles or objects to be cleansed by washing with water, by mixing with the substance finely-pulverized glass, cement, kaolin, or other like substances, either by themselves or combined with finelypulverized marble, witherite, heavy spar, or other like substances, and a solution of a free acid or a metal salt thereof that will in presence of a barium or strontium hydrate form an insoluble metal oxide or hydroxide besides the insoluble barium or strontium salt, and treating the article or object'formed' from such substance with a hot saturated solution of a barium or strontium hydrate.

5. The process herein described of increasing the density of articles or objects made of gypsum, stucco, terra-cotta, and other analogous substances, and adapting such articles or objects to be cleansed by washing with water, by combining silicic-acid anhydrite and combinations.

6. The process herein described of increasing the density of articles or objects made of gypsum, stucco, terra-cotta, and other analogous substances, imparting to such articles or objects a black color, and adapting them to be cleansed by washing with water, by mixing sulphuric acid with the substance from which the article or object is made, and treating such article or object with ahot saturated solution of barium or strontium hydrate combined with an organic substance convertible into carbon by the action of sulphuric acid.

In testimony whereof I affix my signature in presence of two witnesses.

' MAXIMILIAN DENNSTEDT.

Witnesses:

A. DEMELIUS, B. Roi. 

